Is the strain responsible to instability of inorganic perovskites and their photovoltaic devices

Abstract In the past few years, inorganic perovskite compounds including CsPbI3, CsSnI3 and others using as light absorber in emerging solar cells have become one of the most promising research directions to solve the issue of stability faced by their organic-inorganic hybrid halide counterparts. So far, the reported power conversion efficiency of laboratory produced CsPbI3-based perovskite solar cells has exceeded 19%. However, a spontaneous transition of black α-CsPbI3 to non-photosensitive yellow δ-CsPbI3 at room temperature is considered as a serious obstacle of its further application for this material. The phase transition can be induced by strain correlated with the interaction between PbI6 octahedron and Cs+ cation. Therefore, several strategies have been proposed to enhance phase stability of inorganic perovskites and thus the corresponding photovoltaic devices’ performance, such as doping engineering, additives, and dimensionality engineering. We notice that strain is unavoidable in solution-processable perovskite devices of layered structures, and thus may play an important influence on the macroscopic photovoltaic parameters via microscopic effect on crystalline lattice. In this review, we mainly focus on the effect of strain on phase stability of CsPbI3. In this review, we first introduced the type and distribution of strains in this type perovskite material and summarized the causes for this along with common characterization methods. Then we discussed the origin for instability and contribution of strain to phase stability of CsPbI3. The effects of strain on CsPbI3 bandgap and carrier transport were also analyzed. We further outlooked the application prospects and challenges of strain engineering onto CsPbI3 perovskite materials for the purpose of photovoltaic application.